“6.9 times higher than rates in the other high-income countries, driven by firearm homicide rates that were 19.5 times higher. For 15-year olds to 24-year olds, firearm homicide rates in the United States were 42.7 times higher than in the other countries.”

Other interesting studies the report refers to are those that describe possible causes of mass shootings like the one that occurred at Sandy Hook.

One study found that violent video games does increase feelings of aggression in children but cannot be directly linked with murder.

"The evidence strongly suggests that exposure to violent video games is a causal risk factor for increased aggressive behavior, aggressive cognition, and aggressive affect and for decreased empathy and prosocial behavior."

The Center's report pointed out the weakness of studies done on intervening psychologically in individuals who may be capable of mass murders.

Some research has looked at other possible causes to mass shootings such as socioeconomic issues and even seasonal changes.

The recent shootings have even inspired researchers to denote a new kind of serial killer called the pseudocommando.

"The pseudocommando is a type of mass murderer who kills in public during the daytime, plans his offense well in advance, and comes prepared with a powerful arsenal of weapons. He has no escape planned and expects to be killed during the incident. Research suggests that the pseudocommando is driven by strong feelings of anger and resentment, flowing from beliefs about being persecuted or grossly mistreated."